Some liquid storage tanks have an electronic sensor for determining the level of liquid inside the tank. The sensor, located inside the tank, is connected by a wire harness to an indicator gauge located outside the tank. In order to repair or replace the sensor, it is necessary for personnel to remove the necessary access doors and to enter the tank. Prior to entry, the tank must be emptied and ventilated when toxic fumes are present. In some cases preparing the tank for entry can take up to several days. Sometimes, the time required to prepare the tank for entry often exceeds the time required to enter and repair the defective part.
It is desirable therefore to provide a tank liquid level sensing system wherein the sensor can be be removed from the tank without the need for personnel entry into the tank.
A number of conventional quantity sensing systems have been disclosed. For example, U.S. Pat. No. 3,495,915 by Watson et al discloses a removable device for detecting and measuring the size of passages located inside component parts such as turbine blades.
In addition, U.S. Pat. No. 3,656,134 to Brown discloses a liquid level sensor which includes a probe which is movably mounted within a sheath, the sheath including a plurality of guide surfaces for insuring accurate alignment of the probe within the sheath.